A common feature found in many of the refrigerators sold today is an internal water filtering system capable of supplying filtered water to either a drinking dispenser or to an icemaker. In most applications, these filter systems use a filter medium having the capacity to remove chlorine and particulate matter from the source water resulting in cleaner, better tasting water and ice.
When designing these filter systems, an important design consideration is the amount of space that the filter will occupy. This is because any space occupied by the filter will reduce available food storage space within the refrigerator. One way to reduce the space consumed by a water filter system is to use a replaceable cartridge filter. The replaceable cartridge filter typically has enough filtering capacity to last months at a time before it needs to be replaced by a fresh filter.
Previous refrigerator water system designs have included means to protect the water filter by integrating an isolation solenoid valve before the house connection and filter. This valve is only open while filtered water is called for and thus eliminates the potential for flooding in the event of a structural filter failure. In a effort to reduce system complexity and cost, refrigerator manufactures have sought to eliminate the isolation valve and run the filters at a continuous high pressure. One way of replacing the isolation solenoid valve has been to incorporate shut-off means within the filter system itself. One example of such shut-off means is a spring valve within a manifold that closes the water supply line when a filter cartridge is removed.
While the filter shut-off means are effective when a filter cartridge is removed from the system, these shut-off means are ineffective when an event causes a structural failure of the filter cartridge while it is still engaged with the manifold. If a refrigerator lacks the isolation valve, water will continue to flow into and out of the damaged cartridge. The potential exists for such continuous spills to cause damage to flooring in the area surrounding the refrigerator. One way in which a filter cartridge can suffer structural damage is when standing water within the cartridge freezes solid. As the water turns to ice, it expands which can lead to the cracking or bursting of the filter housing.
Present filter cartridge designs utilize conventional, rigid polyolefin polymers, usually unmodified talc-filled polypropylene, due to their fatigue and chemical resistance, low cost, low creep and low toxicity. Unfortunately, these materials tend to have glass transition temperatures that cause them to become brittle at temperatures in the freezing range. In addition to becoming brittle, conventional polypropylene resins have an ultimate elongation percentage of approximately 5-30% while above the glass transition temperature. This combination of limited elasticity and brittleness at freezing temperatures makes polypropylene a less than ideal polymer for use in a refrigerator water filter cartridge that must survive freezing conditions.
The present invention is a freeze resistant filter cartridge assembly, and includes a filter cartridge including a filter housing and a filter media and having at least one component selected from a list of components consisting of:
the filter housing being formed of an increased elasticity polyolefin polymer having elongation and glass transition properties that allow for stretching of the housing during a freezing event rather than rupturing;
a sleeve having volume of air is entrapped therein within and being disposed in the interior of the filter cartridge; and
the filter housing formed of a conventional, rigid polyolefin having a wall thickness great enough to resist freeze induced expansion stresses. The present invention is further a method of forming a freeze resistant filter cartridge assembly.